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ADS1115: Cathodic protection measurement

Part Number: ADS1115
Other Parts Discussed in Thread: ADS1256


We are testing the ADS1115 with ESP32 for Pipe-to-Soil voltage in a cathodic protection monitoring system for buried pipeline.  We could get a quite an accurate reading  with direct connection from the structure and the half-cell(when compared to a calibrated Fluke 87V DMM).

Unfortunately, when we introduce a voltage divider before the input to the ADS1115, the voltage drop quite significantly, varying from 20mV to 100mV.

We are planning to test our setup with ADS1256 as well, but prior to that, we would like to get your professional advice and suggestion as to how to rectify the above problem.